Public Class Form1
    Dim int As Integer = 0

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Refresh()
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Navigate(TextBox.Text)
    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Stop()
    End Sub

    Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoForward()
    End Sub

    Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoBack()
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        AboutBox1.Show()
    End Sub

    Private Sub Button7_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button7.Click
        End
    End Sub

    Private Sub Button8_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button8.Click
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoHome()
    End Sub

    Private Sub AddTabToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles AddTabToolStripMenuItem.Click
        Dim Browser As New WebBrowser
        TabControl1.TabPages.Add("New Page")
        TabControl1.SelectTab(Int)
        Browser.Name = "Web Browser"
        Browser.Dock = DockStyle.Fill
        TabControl1.SelectedTab.Controls.Add(Browser)
        AddHandler Browser.DocumentCompleted, AddressOf Done
        int = +1
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoHome()
    End Sub

    Private Sub DelTabToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles DelTabToolStripMenuItem.Click
        If Not TabControl1.TabPages.Count = 1 Then
            TabControl1.TabPages.RemoveAt(TabControl1.SelectedIndex)
            TabControl1.SelectTab(TabControl1.TabPages.Count - 1)
            int = -1
        End If
    End Sub
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim Browser As New WebBrowser
        TabControl1.TabPages.Add("New Page")
        Browser.Name = "Web Browser"
        Browser.Dock = DockStyle.Fill
        TabControl1.SelectedTab.Controls.Add(Browser)
        AddHandler Browser.DocumentCompleted, AddressOf Done
        int = +1
        CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).GoHome()
    End Sub
    Private Sub Done(ByVal sender As Object, ByVal e As Windows.Forms.WebBrowserDocumentCompletedEventArgs)
        TabControl1.SelectedTab.Text = CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).DocumentTitle
        TextBox.Text = CType(TabControl1.SelectedTab.Controls.Item(0), WebBrowser).Url.ToString
    End Sub

    Private Sub Button9_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button9.Click
        If ColorDialog1.ShowDialog = DialogResult.OK Then
            Me.BackColor = ColorDialog1.Color
        End If
    End Sub

Row 9 gives me that error. The index is at row 50.

A lot of code and little information. For example, what line of code generates the error? Put a try/catch around it and MsgBox the number of elements and the offending index. The index can't be larger than one less than the number of elements.